The image of the watermark on the camera screen is shifted

Question

I created an overlay image for use as a watermark, but the image is shifted. I put the code below, which is based on this message by Ivan Karpan: Real-time watermark image on the camera screen in iphone

- (void)btCamera_TouchUpInside:(UIButton *)button
{
    // Create the image picker controller
    UIImagePickerController *imagePicker = [[UIImagePickerController alloc] init];
    imagePicker.sourceType =  UIImagePickerControllerSourceTypeCamera;
    imagePicker.cameraViewTransform = CGAffineTransformScale(imagePicker.cameraViewTransform, 1.24299, 1.24299);
    imagePicker.allowsImageEditing = NO;
    imagePicker.delegate = self;

    UIImageView * ivWatermark = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Watermark.png"]];
    ivWatermark.alpha = WATERMARK_ALPHA;
    ivWatermark.contentMode = UIViewContentModeTopLeft;
    ivWatermark.frame = self.view.frame;
    imagePicker.cameraOverlayView = ivWatermark;
    [ivWatermark release];

    // Show the image picker
    [self presentModalViewController:imagePicker animated:YES]; 
}

- (void) imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    UIGraphicsBeginImageContext(CGSizeMake(320, 480));
    [(UIImage *)[info objectForKey:UIImagePickerControllerOriginalImage] drawInRect:CGRectMake(0, 0, 320, 480)];
    [[UIImage imageNamed:@"Watermark.png"] drawAtPoint:CGPointMake(0, 0) blendMode:kCGBlendModeNormal alpha:WATERMARK_ALPHA];
    UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
    imageView.image = image;
    UIGraphicsEndImageContext();

    [picker dismissModalViewControllerAnimated:YES];
    UIImageWriteToSavedPhotosAlbum(image, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);

    [picker release];
}

First I create an imagePicker, then I add a watermark to the image of this camera, but the image is shifted. I also tricked scaling according to another post found here: Using Camera on iPad / iPhone with Overlay

In addition, I read other articles about adding an overlay image to the camera image, but they all seem to have the same problem.

Any help would be great?

thank